fix: mail plugin CSRF token handling and trailing slash

- Add CSRF token storage in sessionStorage (persists across reloads)
- Send X-CSRF-Token header on POST/PATCH/DELETE requests
- Store CSRF token on login, clear on logout
- Fix trailing slash in mail list API call (/mail/ -> /mail)

frontend/src/api/client.ts

@@ -15,6 +15,23 @@ export const apiClient = axios.create({
   },
 });
 
+// CSRF token storage — persisted in sessionStorage, sent on all unsafe methods
+const CSRF_KEY = 'leocrm_csrf_token';
+let csrfToken: string | null = sessionStorage.getItem(CSRF_KEY);
+
+export function setCsrfToken(token: string | null) {
+  csrfToken = token;
+  if (token) {
+    sessionStorage.setItem(CSRF_KEY, token);
+  } else {
+    sessionStorage.removeItem(CSRF_KEY);
+  }
+}
+
+export function getCsrfToken(): string | null {
+  return csrfToken;
+}
+
 let onUnauthorized: (() => void) | null = null;
 let onValidationError: ((errors: Record<string, string[]>) => void) | null = null;
 
@@ -28,6 +45,11 @@ export function setValidationErrorHandler(handler: (errors: Record<string, strin
 
 apiClient.interceptors.request.use(
   (config: InternalAxiosRequestConfig) => {
+    // Attach CSRF token on unsafe methods
+    const unsafe = ['post', 'put', 'patch', 'delete'];
+    if (unsafe.includes(config.method?.toLowerCase() ?? '') && csrfToken) {
+      config.headers['X-CSRF-Token'] = csrfToken;
+    }
     return config;
   },
   (error) => Promise.reject(error)

frontend/src/api/hooks.ts

@@ -1,5 +1,5 @@
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
-import { apiPost, apiGet, apiPatch, apiDelete, apiClient } from './client';
+import { apiPost, apiGet, apiPatch, apiDelete, apiClient, setCsrfToken } from './client';
 import { useAuthStore } from '@/store/authStore';
 
 export interface LoginPayload {
@@ -112,6 +112,10 @@ export function useLogin() {
     onSuccess: (data: any) => {
       setUser(data.user || data);
       setError(null);
+      // Store CSRF token for subsequent unsafe requests
+      if (data.csrf_token) {
+        setCsrfToken(data.csrf_token);
+      }
     },
     onError: (error: any) => {
       setError(error.message || 'Login failed');
@@ -126,6 +130,7 @@ export function useLogout() {
     mutationFn: () => apiPost('/auth/logout'),
     onSettled: () => {
       logout();
+      setCsrfToken(null);
       queryClient.clear();
     },
   });

frontend/src/api/mail.ts

@@ -401,7 +401,7 @@ export function deleteFolder(folderId: string): Promise<void> {
 
 export function fetchMails(folderId: string, page: number): Promise<MailListResult> {
   const qs = new URLSearchParams({ folder_id: folderId, page: String(page) }).toString();
-  return apiGet<MailListResult>(`/mail/?${qs}`);
+  return apiGet<MailListResult>(`/mail?${qs}`);
 }
 
 export function getMail(mailId: string): Promise<Mail> {